Method of centrifugally separating ice crystals from an aqueous solution



Dec. 1 7, 1968 N. GANIARIS 3,416,661

METHOD OF CENTRIFUGALLY SEPARATING ICE CRYSTALS FROM AN AQUEOUS SOLUTION Original Filed Dec. 6, 1965 2 Sheets-Sheet 1 INVENTOR NEOPHYTOS GANINUS jw-Mgm Dec. 17, 1968 N. GANIARIS METHOD OF CENTRIFUGALLY SEPARATING ICE CRYSTALS FROM AN AQUEOUS SOLUTION 2 Sheets-Sheet 2- Original Filed Dec. 6.

FIG. 2

IN VE NTOQ NEOPHYTOS GAN\AR\$ United States Patent METHOD OF CENTRIFUGALLY SEPARATING ICE CRYSTALS FROM AN AQUEOUS SOLUTION Neophytos Ganiaris, Riverdale, N.Y., assignor to Struthers Scientific and International Corporation, New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 511,951, Dec. 6, 1965. This application Oct. 25, 1966, Ser. No. 589,458

1 Claim. (Cl. 210-78) ABSTRACT OF THE DISCLOSURE An improved method for contrifugally separating ice crystals from an aqueous solution wherein ice build-up on the exterior surface of the feed conduit and on the interior surface of the centrifuge housing is prevented by heating these surfaces above 32 F.

This application is a continuation of my prior copending application Ser. No. 511,951, filed Dec. 6, 1965 and now abandoned.

The present invention relates to centrifuges, and particularly to centrifuges of the type employed for the separation of solids from liquids. Still more particularly, the present invention relates to centrifuges which are designed to separate ice crystals from an aqueous mother liquor.

Centrifuges designed for liquid-solid separation may be of various shapes and mechanical designs. The centrifuge bowl may, for example, be of the basket type and may have a perforate or an imperforate wall. In many cases, the bowl may be provided with an internal scroll or screw mechanism which serves to advance the separated solids toward the discharge outlet of the bowl.

The known centrifuges for liquid-solid separation have presented a number of problems in operation when used for separation of ice from a slurry. Particular problems have arisen in connection with the procedures for introducing the slurry onto the feed end of the basket. Thus, for example, in the case of centrifuges which employ a scroll, the slurry is directed through one or more openings in the wall of the scroll to the feed end of the basket interior. Due to mechanical consideration, the slurry is directed to the feed end through a feed conduit which enters the centrifuge housing through the discharge -end of the device. Due to temperature differences in the interior, ice often builds up on the exterior of the feed pipe and eventually completely plugs the discharge end of the centrifuge.

Further, in order to effectively remove ice from the centrifuge, it has been found desirable to re-slurry the purified ice in Water or other carrier introduced as a spray at the discharge end of the basket. Splashing in the operation often causes an ice build-up on the interior of the casing wall which may also cause eventual shut down of the machine.

It is therefore an object of the present invention to provide an improved centrifugal method of separating ice crystals from an aqueous solution.

This and other objects and advantages of the present invention will become more apparent from the following description thereof:

FIG. 1 is a side elevation, being partly in section, of a centrifuge constructed in accordance with the invention;

FIG. 2 is a vertical section along the lines 22 of FIG. 1.

Referring to the drawings, and particularly to FIG. 1, a centrifuge is shown, being designed for the separation of solids from liquids. The centrifuge 10 is equipped with a cylindrical bowl, or basket 12, which is rotatably mounted within a housing 14, and provides a centrifuge ice chamber 16. Positioned within the chamber 16 is a scroll 18. The scroll 18 is mounted coaxially with, and is retatable with respect to, the basket 12.

The basket 12 is rotated by a belt 20 which is driven by conventional means (not shown) such as a motor. The belt 20 serves to drive a pulley 22 which is mounted on a supporting shaft structure 24 for the basket 12.

The scroll 18 is similarly rotated by a belt 2-6, which drives a pulley 28 mounted on supporting shaft structure 30 for the scroll 18. However, the belt 26 is driven at a speed slightly greater than that of the belt 20. The driving mechanism (not shown) for the belt 26 may be of any conventional design. For example, the belt 26 may be driven, through use of a differential gear mechanism, by the same drive means as employed for driving the belt 20.

The basket 12 is provided with a cylindrical side wall 32 and is closed at the drive end by a wall 34. An opening 35 is cut through the wall 34 for receipt therethrough of the respective inner ends 36 and 3-7 of the supporting shaft structures 24 and 30. At its end opposite the wall 34, the basket 12 is open as seen at 38. The side wall 32 is formed at the open end 38 with a circumferentially extending lip 39. The side wall 32 of the basket 12 is provided, over a portion 40 thereof, with perforations 42.

A cylindrical lining screen 44 lies within the chamber 16, and in contact with the side Wall 32. This screen serves to retain small particles of solids within the basket 12.

The scroll 18 is of generally hollow cylindrical shape, and is closed at one end by a wall 56. At its opposite end, the scroll 18 is open as seen at 58. The side wall 60 of the scroll 18 at its outer circumferential surface 61 is provided with a continuously extending helical impeller blade 62. The latter is of such pitch diameter that the distal edge 64 thereof is located closely adjacent the screen 44. The rearward end of the blade 62 is located generally in alignment with the end Wall 56. The forward end 68 of the blade 62 is located adjacent the open end 58 of the scroll 18. The scroll 18 is positioned so that the Wall 56 and the rearward end of the blade 62 lie closely adjacent the end wall 3 4 of the basket 12.

The scroll 18 is shown to be of abbreviated length, as compared to the length of the chamber 16. Thus, the open end 58 of the scroll 18 is spaced from the open end 38 of the basket 12. At the same time, the forward end 68 of the blade 62 is spaced from the lip 39 of the side wall 32 of basket 12. It will thus be seen that only the rearward portion 17 of the chamber 16, located adjacent to the end wall 34, is occupied by the scroll 18. The latter does not extend through the remaining portion 19 of chamber 16, located adjacent to the open end 38 of basket 12. The blade 62 overlies only that portion 45 of the screen 44 which is coextensive with the chamber portion 17. The remaining screen portion 46, lying adjacent the lip 39, provides a washing zone for separated solids, as will be made clear hereinbelow.

A feed conduit 70 extends through the open end 38 of the basket 12. At its inner end 72 the conduit 70 extends through the open end 58 of the scroll 18.

A comically-shaped baflie member is mounted within the scroll 18. The baffie member, at its inner or constricted end, is located at the open end 58 of the scroll 18 and there receives the inner end 72 of the feed conduit 70. At its outer, or flared, end the baflle member is secured in conventional manner to the scroll side wall 60 and at a short distance from the end wall 56. A number of discharge ports 82 are spaced about the scroll wall 60. The discharge ports 82 are each located between end wall 56 of the scroll 18 and the flared end 80 of the baflie member.

A conduit 84 for conducting wash liquid extends through the open end 38 of the basket 12 and into the chamber 16. The conduit 84 at its inner end is provided with a nozzle 86. The nozzle 86 is positioned so as to be close to the upper surface of the cake of solids advanced across the portion 46 of the screen 44.

The housing 14 is made up of two sections, 13 and 15. The first housing section 13 generally serves to enclose the basket 12. The housing section 13 is formed of a circumferentially-extending wall 92 and two oppositely-positioned side walls 93 and 94. The latter two walls each extend generally radially with respect to the axis of the housing 13. The side wall 93 is provided with a central, circular opening 95 which is designed to permit the passage therethrough of the shaft structure 24 of the basket 12 and the shaft structure 30 of the scroll 18. The wall 94 is provided with a circular opening 96, within which the lip 39 of the basket 12 is situated.

The housing section 13 is divided by a radially-extending divider plate 97 into two chambers 98 and 99. The chamber 98 is situated to receive liquid which has been separated from solids, in the operation of the centrifuge 10. Such separated liquid is received from the chamber portion 17 and through the screen portion 45 and adjacently located perforations 42 in the basket side wall 32. Located in the chamber 98 and mounted on the circumferential wall portion 92 of the housing section 13 may be a plurality of circumferentially spaced spray nozzles 100 (one being shown). Each nozzle 100 is connected through a conduit 102 to a distributor head (not shown). The nozzles 100 are positioned to direct wash liquid, such as water, onto the exterior surface 104 of the basket wall 32. Such Wash liquid serves to maintain the perforations 42 clear for free flow therethrough of the liquid separated from the solids. The wash nozzles 100 are operative intermittently and as required to keep the perforations 42 clear of debris. Continuous use of the nozzles 100 serves to dilute the mother liquor and may be undesirable when the mother liquor is the desired product.

An outlet pipe 106 serves to conduct the separated liquid from the chamber 98. The outlet pipe 106 extends horizontally from a lower portion of the chamber 98 and terminates in a downwardly-directed discharge end 107.

The chamber 99 is situated to receive wash liquor which has been formed by washing of the separated solids by wash liquid from the nozzle 86. Such wash liquor is received from the chamber portion 19 and through the screen portion 46 and adjacently located perforations 42. A horizontal outlet pipe 108, having a downwardlydirected outer end 109 extends from a bottom portion of the chamber 99 for the discharge of the wash liquor.

The housing section is formed by the wall 94; a circumferentially-extending wall 110; and an outer end Wall 111. The section 15 provides therewithin a generally cylindrical chamber 112 (see also FIG. 2) situated to receive washed solids which pass from the chamber 19. Mounted on an upper portion of the wall 110 and located at opposite sides of the chamber 112 are two water inlet couplings 114 and 116 connected to water inlet conduits 118 and 120 respectively. A spray pipe 122, having perforations 123 in the wall thereof, is connected at its opposite ends 124 and 126 to the couplings 114 and 116 respectively. The spray pipe 122 serves to spray liquid, such as water, onto the solids received in the chamber 112. Such liquid carries the solids from the chamber 112 and through a discharge outlet 128.

The housing 14 is designed to permit rotation therewithin of the basket 12. Thus, a small clearance is provided between the shaft structure 24 for the basket 12 and the circumferential surface 130 defining the opening 95 in the side wall 93 of the housing 14. A small clearance is likewise provided between the outer circumferential surface 132 of the lip 39 and circumferential surface 134 defining the opening 96 in the side wall 94 of the housing 14.

In the operation of the centrifuge 10, feed slurry constituted of a mixture of solids and liquid to be separated is fed through the feed conduit 70 and from the inner end 72 thereof into the scroll 18. The feed slurry proceeds along the inner surface of the bafile member, through the discharge ports 82, and onto the screen portion 45. Here, solids and liquid are separated by the centrifugal forces. The separated liquid passes through the screen portion 45, through the adjacent wall perforations 42, and into the chamber 98. Such separated liquid is then withdrawn from the chamber 98 through the discharge pipe 106. The separated solids, possibly retaining some adherent liquid, remain on the screen portion 45.

The washed solids pass from the screen portion 46 over the lip 39 and into the chamber 112. From the chamber 112, the solids are discharged through the outlet 128. Such discharge is aided by liquid from the spray pipe 122.

The basket 12 is preferably rotated at a speed that will provide a force of LOUD-1,500 gs. The scroll 18 is, as has been indicated, rotated at a speed slightly greater than that of the basket 12. The preferred speed difference is about 2 to 10 r.p.m. As a result of the speed of rotation of the basket, adequate dewatering of the solids is assured. At the same time, the rotation of the scroll 18 relative to the basket 12 provides for advancement of the separated solids by the blade 62 along the screen portions 45 and 46 and over the lip 39.

When the centrifuge is employed to separate ice from a concentrated solution (such as, for example, sea water brine concentrated to seven percent dissolved salt, or orange juice or coffee brew which has been concentrated by freezing) the temperature within the device is usually well below 32 F. at the feed or mother liquor end. When the ice is washed with water or solution of a concentration lower than that of the mother liquor, the temperature at the discharge end of the centrifuge is closer to the melting point of pure ice. Because the feed conduit passes through the discharge end of the centrifuge and as the interior of the feed pipe is colder than its outside environment, there is a tendency for ice to form on the outside of the feed conduit. In order to prevent ice build up on the feed pipe; it has been found, in accordance with this invention, that the feed conduit can be heated by external means along its length (or a portion thereof) from the entry point through the casing wall to near its terminal point at the constricted end 76 of the conical bafiie. By maintaining the exterior wall of conduit 70 above the temperature of the slurry passing through it, the tendency for ice to form on, or adhere to, the exterior of the conduit 70 is eliminated.

The heating means 73 used to adjust the temperature of the outside of conduit 70 can comprise a fluid heating coil wrapped as a helix around conduit 70. It can take the form of a small diameter tube 73 through which warm or rot water (or other suitable liquid) is circulated to maintain the exterior of conduit 70above the freezing point of water. Alternatively, the heating means 73 may comprise an electrical heating element or a plurality of heating elements wrapped around the conduit 70.

The tendency for ice to form on and adhere to the conduit 70 can also be eliminated or substantially reduced by fabricating the conduit 70 so that the exterior surface thereof is a material to which ice will not readily adhere. This may be accomplished by coating the exterior surface of conduit 70 with appropriate material or by fabricating the conduit entirely from such material.

Suitable materials for coating or fabricating the conduit 70 comprise relatively non-wett-able solid polymeric organic compositions (either thermoplastic or thermosetting) which have the ability to form a relatively smooth surface and which have relatively low coefiicients of friction and which are relatively good thermal insulators. These materials include polymers such as halogenated polyethers, halogenated lower alkyl hydrocarbon polymers (including, for example, poly tetrafluoroethylene, poly perfiuorochloroethylene, polyvinyl chloride), polymeric alkyl hydrocarbons (such as, for example, polyethylene, polypropylene and higher polyolefins), polyurethane polymers and copolymers, epoxy polymers, silicones and polysiloxanes. Polysiloxanes and poly perhalogenated hydrocarbon polymers are preferred materials because they meet the requirements set forth above. Poly tetrafluoroethylene is a particularly preferred material inasmuch as excellent results in the prevention of ice adhesion have been achieved with its use.

During operation of the centrifuge, ice leaving the basket 12 flows over the lip 39 and is re-slurred in water or other suitable carrier to be discharged through the discharge 128. The re-slurry liquid is sprayed from the holes 123 in the pipe 120. The rapid rotation of the centrifuge basket and the splashing caused by the spray often leads to the depositing of ice around the periphery of the chamber 112; for example, on the outer wall 111 of the casing 15 and the circumferential housing wall 110- of the casing 15. To prevent this undesirable ice buildup, it has been found that the exterior surfaces of the casing near the discharge end of the centrifuge can be heated or warmed by an appropriate heating means 50. As with the heating means used to adjust the temperature of the outside of the heat conduit 70, the heating means 50 can comprise a fluid heating coil positioned against the casing 15 around the outer circumferential surface 110 and in addition, if desired or necessary, along the outer surface 111. The heating means 50 can take the form of a small diameter tube through which warm or hot water (or other suitable liquid) is circulated to maintain the temperature of the casing above the freezing point of pure water so that ice will not adhere to the interior surfaces thereof. Alternatively, the heating means 50 may comprise an electrical heating element or a plurality of heating elements spaced so as to obtain the desired result.

As a further alternate, the outside of the centrifuge casing 15 may be heated by spraying the exterior portion with warm air or warm water through a suitable spray couduit 51. Thus, one or more conduits, terminating in spray nozzles, may be used to keep the centrifuge housing 15 at above the temperature at which ice will adhere by spraying warm water on the housing or by circulating warm air over the exterior portion.

In accordance with the present invention, a number of modifications may be effected with respect to the structure and operation of the centrifuge 10. Thus, the basket 12 and the scroll 18 may be designed of a shape other than cylindrical, e.g., conical. Also, the basket 12 may be formed with a solid rather than perforated side wall 32. In this case, suitable ports, as are well known in the art, would be provided for the passage of the mother liquor from the chamber 16. Further, the scroll 18 may be coextensive with the basket 12 and may contain wash ports instead of the nozzle 86. Still further, when the basket is conical in form, the scroll may be completely eliminated and the conical bafile may be fixed to the end 72 of feed conduit 70.

Although the invention has been described with reference to particular embodiments thereof, it will be realized that various changes may be made therein without departing from the spirit of the invention or the scope of the appended claim.

1. In a method of separating ice crystals from an aqueous solution in a centrifuge, the steps comprising:

rotating a perforate centrifuge basket having an open discharge end within an imperforate housing having an inner surface and an outer surface;

feeding a mixture of ice and aqueous solution to said basket through a feed conduit having an inner surface and an outer surface and being located within the housing with a portion extending into said discharge end of the basket; and

separately discharging ice and aqueous solution from said basket;

the improvement which consists of maintaining the outer surface of said feed conduit and the inner surface of said housing substantially free from ice accumulation by heating said outer surface above 32 F.

References Cited UNITED STATES PATENTS 2,354,633 7/1944 Bedford 2l0-71 X 2,631,728 3/1953 Popp 210-179 X 2,720,313 10/1955 Pattison 210-479 X 2,977,234 3/ 1961 Wenzelberger 210-71 3,199,681 8/1965 Kirkpatrick 210-377 X REUBEN FRIEDMAN, Primary Examiner.

J. L. DE CESARE, Assistant Examiner.

US. Cl. X.R. 

